Embodiments of the present invention claim priority from Japanese Patent Application Ser. No. H11-295247, filed Oct. 18, 1999, and Japanese Patent Application Ser. No. 2000-150040, filed May 22, 2000. The content of these applications are incorporated by reference herein.
1. Field of the Invention
The present invention relates to an audio waveform reproduction apparatus for storing an audio waveform having its own tempo, for example, by sampling, and reproducing the audio waveform, changing the tempo to a reproduction tempo that can be specified as desired at the time of reproduction. The reproduction tempo can be tempo information that is input externally (for example, the timing clock, which is a system real-time message represented by F8 in the case of a MIDI signal) or internal tempo information specified inside the apparatus, and the apparatus can reproduce the waveform at a reproduction speed that corresponds to this tempo information.
2. Description of the Related Art
Conventionally, to reproduce sampled audio waveforms, several time axis compression/expansion techniques are known that change the reproduction speed without changing the pitch, and these time axis compression/expansion techniques are used to change the original tempo of the audio waveform (that is, the tempo at the time of the recording) to a desired tempo when reproducing the sampled audio waveform.
For example, in the invention disclosed in Publication of Unexamined Japanese Patent Application (Tokkai) H7-295589, to reproduce the sampled audio waveform with time axis compression/expansion so as to change the tempo at the time of recording to a desired reproduction tempo, the ratio of the original tempo of the audio waveform (that is, the tempo at the time of recording) and the tempo for reproduction is determined, and taking this ratio as the time axis compression/expansion amount, the audio waveform is compressed/expanded on the time axis, and the original audio waveform is reproduced at the reproduction speed of the reproduction tempo.
However, to reproduce the audio waveform with this method, first of all, the amount for the time axis compression/expansion processing is determined and set beforehand, and this amount for the time axis compression/expansion processing is sustained for the duration of the waveform reproduction. On the other hand, the tempo of music usually changes somewhat over the passage of time. Therefore, with the proceeding reproduction of the audio waveform, a discrepancy to the set tempo ratio occurs, which builds up, thus deviating from the tempo, so that it was difficult to reproduce an audio waveform that follows a change of the tempo over time. Neither was it possible to reproduce audio waveforms following a reproduction tempo when the reproduction speed was changed during the reproduction (for example, by changes due to speed indicators such as xe2x80x9critardandoxe2x80x9d or xe2x80x9caccelerandoxe2x80x9d).
With the foregoing in mind and in light of these problems, it is an object of the present invention to provide a device for reproducing recorded audio waveforms that does not deviate from the tempo when the reproduction is performed at a desired tempo that is different from the tempo at the time of recording.
Another object of the present invention is to provide a device for reproducing recorded audio waveforms that precisely follows temporal changes of the tempo, and, in particular, one that can precisely follow temporal changes of the tempo information in a realtime process.
In order to attain these objects, an audio waveform reproduction apparatus in accordance with the present invention includes (1) a storage means for storing waveform data representing an audio waveform, (2) a reproduction tempo information input means for inputting reproduction tempo information expressing a tempo for a time when the audio waveform is reproduced, (3) a first time function production means for producing first information (TP) that is a time function based on the reproduction tempo information, (4) a second time function production means for producing second information (PP) that is a time function based on time axis compression/expansion information (TR), (5) a time axis compression/expansion information production means for comparing the first information and the second information and calculating the time axis compression/expansion information (TR) towards matching the temporal change of the second information with the temporal change of the first information, and (6) a time axis compression/expansion processing means for subjecting the audio waveform to time axis compression/expansion processing based on the time axis compression/expansion information (TR) to produce a reproduction audio waveform. The first information (TP) and the second information (PP) represent positions on a common axis.
An audio waveform reproduction apparatus with this basic configuration produces time axis compression/expansion information precisely following temporal changes of the reproduction tempo at which the recorded audio waveform is reproduced, and subjects the recorded audio waveform to time axis compression/expansion processing in accordance with this time axis compression/expansion information, so that the audio waveform can be reproduced, precisely following temporal changes of the reproduction tempo information.
That is to say, waveform data representing the audio waveform and original tempo information, which is the tempo at the time of recording of the audio waveform, are stored beforehand in a memory means. Reproduction tempo information, which represents the tempo at the time of reproduction of the audio waveform, is input with a reproduction tempo information input means.
The first time function production means produces first information (TP) that is a time function of the reproduction tempo information, and the second time function production means produces second information (PP) that is a time function of time axis compression/expansion information (TR).
The time axis compression/expansion information production means compares the first information and the second information and calculates the time axis compression/expansion information (TR) towards matching the temporal change of the second information with the temporal change of the first information. By successively calculating the time axis compression/expansion information (TR) in this manner, the time axis compression/expansion processing means subjects the audio waveform to time axis compression/expansion processing based on the time axis compression/expansion information (TR) to reproduce the recorded audio waveform, precisely following the temporal changes of the reproduction tempo information.
It is preferable that in the audio waveform reproduction apparatus with this basic configuration, the waveform data of the storage means is PCM data, which is a time series of sampled amplitude data of the audio waveform, and that the time axis compression/expansion processing means subjects the PCM data to time axis compression/expansion processing based on the time axis compression/expansion information (TR) to produce the reproduction audio waveform.
In this configuration, it is preferable that the common axis represents positions of the PCM data in terms of addresses.
In this configuration of the audio waveform reproduction apparatus, it is preferable that the storage means also stores original tempo information, which is the tempo of the audio waveform at the time of recording, that the reproduction tempo information is period information of a period corresponding to the reproduction tempo, that the first time function production means calculates the amount of change of addresses per predetermined number of periods of reproduction tempo information, based on the original tempo information, and produces the first information, which is a time function representing positions of the PCM data, based on the amount of change of addresses and the reproduction tempo information.
In this configuration of the audio waveform reproduction apparatus, it is preferable that the first time function production means calculates the amount of change of addresses per one period of the reproduction tempo information and produces the first information (TP), which is a time function representing positions of the PCM data, which advance successively by the amount of change every time the reproduction tempo information is input, that the second time function production means produces the second information (PP), which is a time function representing positions of the PCM data, which advance successively by the time axis compression/expansion information (TR) for each reproduction sampling period, and that the time axis compression/expansion information production means compares the first information (TP) and the second information (PP) for each reproduction tempo information to calculate the time axis compression/expansion information (TR), which is the advance amount towards matching the first information with the second information.
In the aforementioned basic configuration of the audio waveform reproduction apparatus, it is preferable that the waveform data of the storage means is analysis data for analyzing and representing the audio waveform and that the time axis compression/expansion processing means subjects the analysis data to time axis compression/expansion processing based on the time axis compression/expansion information (TR) to produce the reproduction audio waveform.
In this configuration, it is preferable that the common axis represents positions in terms of virtual addresses representing the time axis of the audio waveform.
In this configuration of the audio waveform reproduction apparatus, it is preferable that the storage means also stores original tempo information, which is the tempo of the audio waveform at the time of recording, that wherein the reproduction tempo information is period information of periods corresponding to the reproduction tempo, and that the first time function production means calculates the amount of change of addresses per predetermined number of periods of reproduction tempo information, based on the original tempo information, and produces the first information, which is a time function representing positions in terms of the virtual addresses, based on the amount of change of addresses and the reproduction tempo information.
In this configuration of the audio waveform reproduction apparatus, it is preferable that the first time function production means calculates the amount of change of addresses per one period of the reproduction tempo information and produces the first information (TP), which is a time function representing positions in terms of the virtual addresses, which advance successively by the amount of change every time the reproduction tempo information is input, that the second time function production means produces the second information (PP), which is a time function representing positions in terms of the virtual addresses, which advance successively by the time axis compression/expansion information (TR) for each reproduction sampling period, and that the time axis compression/expansion information production means compares the first information (TP) and the second information (PP) for each reproduction tempo information to calculate the time axis compression/expansion information (TR), which is the advance amount towards matching the first information with the second information.
In this configuration of the audio waveform reproduction apparatus, it is preferable that the production of the audio waveform with the time axis compression/expansion processing means is repeated from the start position of the audio waveform, at a predetermined repetition period that is based on the reproduction tempo.
These and other objects, features, and advantages of embodiments of the invention will be apparent to those skilled in the art from the following detailed description of embodiments of the invention, when read with the drawings and appended claims.